For example, in facilities such as thermal power plants where flue gas as combustion exhaust gas is produced, an exhaust gas treatment apparatus (desulfurization apparatus) treating exhaust gas in fuel gas is provided for the purpose of preventing air pollution due to flue gas containing sulfur oxide (SOx) such as sulfurous acid gas (SO2).
As a kind of such an exhaust gas treatment apparatus, there has been widely known one in which sulfurous acid gas (SO2) contained in exhaust gas is in contact with an absorbing liquid consisting of an aqueous solution (sulfurous acid gas neutralizer slurry solution) dissolved or suspended with limestone (CaCO3) and reacted and absorbed in the absorbing liquid (for example, see Patent Literature 1).
FIG. 5 shows a configuration of a main portion of this type of conventional desulfurization apparatus. A sealed vessel (absorption tower) 1 constituting the main portion of the desulfurization apparatus has an upper stage deck (upper partition) 3 and a lower stage deck (lower partition) 2 arranged vertically at a distance from each other. The decks 2 and 3 are provided as partitions defining an inlet gas introducing space of the sealed vessel 1. A lower space of the lower stage deck 2 serves as an absorbing liquid storage portion (storage vessel) 4, a space between the upper stage deck 3 and the lower stage deck 2 is an exhaust gas introducing portion 6, and an upper space of the upper stage deck 3 serves as an exhaust gas deriving portion 8. The absorbing liquid storage portion 4 stores therein an absorbing liquid K, consisting of aqueous slurry of limestone, at a predetermined liquid level. An exhaust gas introducing portion 6 is connected to an inlet duct 5 through which exhaust gas is introduced into the sealed vessel 1, and the exhaust gas deriving portion 8 is connected to an outlet duct 7 through which treated exhaust gas in the sealed vessel 1 is derived outside. The inlet duct 5 is provided with a gas cooling portion 17 which circulates and supplies a portion of the absorbing liquid K from a cooling line 11 by means of a pump 13 and is equipped with spray nozzles 16 for spraying the absorbing liquid as cooling water against the introduced exhaust gas and cooling the exhaust gas.
A larger number of openings (through-holes) are dispersively bored in the lower stage deck 2, and the through-holes are connected to upper end portions of the sparger pipes 9 hanging on a lower surface of the lower stage deck 2. The sparger pipes 9 extend downward, and their lower ends are inserted into the absorbing liquid K in the absorbing liquid storage portion 4 so that exhaust gas is ejected and dispersed under a liquid level of the absorbing liquid K.
Gas risers 10 placing an upper space 4a above the liquid level of the absorbing liquid in the absorbing liquid storage portion 4 in communication with the exhaust gas deriving portion 8 are provided between the lower stage deck 2 and the upper stage deck 3 so as to pass through the exhaust gas introducing portion 6. An air supply pipe (not shown) through which oxidation air is ejected and a mixer (not shown) for mixing the absorbing liquid K are provided on the bottom portion side of the absorbing liquid storage portion 4, and a blower (not shown) for pressure feeding air is connected to a base end side of the supply pipe.
The sealed vessel 1 is connected to a supply line for supplying an absorbing liquid for supply (limestone as an absorbent) into the sealed vessel 1.
A spray nozzle 18 is disposed above the sparger pipe 9 in order to wash out gypsum adhered to a surface of the gas riser 10 as described later and a mass of gypsum dropped on the sparger pipe 9 from the gas riser 10, and spray nozzles 19 are disposed around the gas riser 10. A filtrate obtained when gypsum is separated from the absorbing liquid as described later is supplied to the spray nozzles 18 and 19 through a pipe and intermittently sprayed.
In the sealed vessel 1 having the above constitution, when exhaust gas is fed from the inlet duct 5 to the exhaust gas introducing portion 6 while oxygen (air) is supplied into the absorbing liquid K through the supply pipe, the exhaust gas is ejected from ejection holes of the lower ends of the sparger pipes 9 and violently mixed with the absorbing liquid K, and a liquid phase continuous froth layer (jet bubbling layer) is formed. At this time, the mixer is rotated to mix the absorbing liquid K, and, at the same time, oxidation air supplied from the supply pipe is continuously supplied into the absorbing liquid K from a nozzle at a tip end of the supply pipe. Consequently, highly efficient gas-liquid contact is performed in the froth layer, and as shown by SO2+CaCO3+1/2O2+H2O→CaSO4.2H2O↓+CO2↑, sulfurous acid gas (SO2) contained in exhaust gas is oxidized. At the same time, a reaction in which sulfurous acid gas is neutralized with limestone in the absorbing liquid K takes place, and the sulfurous acid gas is absorbed and removed. Exhaust gas thus desulfurized reaches the exhaust gas deriving portion 8 through the gas risers 10 from a space above the liquid level of the absorbing liquid storage portion 4 (above the froth layer) to be passed through the outlet duct 7 from the exhaust gas deriving portion 8, and, thus, to be discharged outside from an exhaust flue. The outlet duct 7 is provided with an eliminator (not shown) which removes mist (water droplets) containing the above-described slurry.
On the lower stage deck 2, a large number of through-holes are substantially evenly dispersed and arranged as described above, and the sparger pipes 9 are provided in the respective through-holes. Further, the gas risers 10 are substantially evenly dispersed and arranged so that the gas riser 10 is arranged for each of the substantially predetermined number of the sparger pipes 9, and several hundred gas risers 10 may be provided, for example, although the number is one figure lower than the number of the sparger pipes 9.